To absorb fluctuations in the price and supply of silver that is indispensable to silver halide photographic materials, intensive efforts are being made to reduce the use of silver or entirely eliminate it. But to produce a silverless photographic material for radiography that has both high sensitivity and high image density is almost impossible, and instead there is a great need for reducing the silver content of the material. However, reducing the silver content while maintaining the sensitivity of the existing black-and-white X-ray film with an emulsion coating on both sides is very difficult without reducing the maximum image density and impairing the granularity of silver halide grains and the sharpness of image.
Among the methods known to produce a photographic image of high density by using less silver is the silver salt diffusion transfer (DTR) process. This method is recognized as being very effective in silver reduction because it provides a transfer image having a very high covering power and hence achieves high sensitivity, image density and sharpness with reduced silver content. But the DTR process is a positive-positive process and provides a positive final image. Therefore, this process cannot be applied to an X-ray film that forms a negative image as an information source for diagnosis.
Japanese Patent Publication No. 3835/70 describes a diffusion transfer process that uses less silver and forms a developing negative image by using a processing solution containg a solubility increasing agent that is capable of forming an insoluble complex compound with silver halide. But the negative image produced by this process is by no means completely satisfactory. Japanese Patent Application (OPI) No. 48544/79 (the symbol OPI as used herein means an unexamined published Japanese patent application) describes a new negative image forming method which uses a photographic element wherein a photosensitive silver halide layer (1) is combined with a layer (2) of metal salt grains that are more soluble than the silver halide grains of layer (1) and which are substantially devoid of sensitivity and on which a solubility decreasing agent is adsorbed and with a layer (3) of physical developing nuclei. When this element with a silver halide layer formed on one side is directly applied to a photographic material for radiography of the type contemplated by the present invention, both the fixing speed and the film drying speed are delayed; the former is delayed because of the silver coating weight and the solubility reducing agent (to be described later), and the latter is prolonged due to the total binder content. As a result, if the element is subjected to rapid processing (90 seconds) by the common X-ray automatic processor, insufficient fixing produces a stained silver image or causes discoloration during storage, and no satisfactory diagnostic information is obtained. Furthermore, insufficient drying causes film blocking or transfer of streaks from the squeegee rollers onto the image.